(化工专业英语)unit2 lesson 2Pumping of Fluids.ppt

Unit 2 (2)Pumping of Fluids Correction: 1.P. 35 line 1 from bottom, “specialist” should be read “special” 2.P. 36 line 3 from bottom, “enthaply” should be read “enthalpy” 3.P. 37 line 1, “as” should be read “gas” 4.P. 38 line 12 from bottom, “With suspensions.” should be read “ With suspensions,” 5.P. 38 line 5 from bottom, “stean” should be read “steam” 6.P. 39 line 10, “vavles” should be read “valves” 7.P. 39 line 11, “ags” should be read “gas”lFor the pumping of liquids or gases from one vessel容器to another or through long pipes, some form of mechanical pump is usually employed使用，雇佣.l对于从一个容器到另一个容器或通过长的 管道输送液体或气体，通常需要采用某种 形式的机械泵。

lThe energy required by the pump will depend on the height through which the fluid is raised, the pressure required on delivery递送，传输 the length and diameter直径of the pipe, the rate of flow, together with the physical properties of the fluid, particularly its viscosity粘度and density密度. l泵所需的能量取决于流体被提升的高度、需要 输出的压力、管道的长度与直径以及流速和流 体的物理性质，尤其是它的粘度和密度lThe pumping of liquids such as sulphuric acid( 硫 酸sulfuric acid )or petroleum石油products like benzene苯or naphtha石脑油from bulk store原料 仓库to process buildings, or the pumping of fluids round绕行, 完成reaction units and through heat exchangers热交换器, are typical illustrations例子 ，图示of the use of pumps.l例如从原料库向生产装置中输送硫酸或输送苯 和石脑油这些石油产品，或者输送这些流体通 过反应单元和通过热交换器，这些都是使用泵 的典型例子。

lThe pumping of crude oil原油or natural gas天然气over long distances, or of fluids from one section of a works to another, are further更远的，更进一步的 example. l远距离输送石油或天然气，或从工厂的一个 工段向另一个工段输送流体，是另外的例子 lOn the one hand, it may be necessary to inject 注射，注入reactants反应物or catalyst into a reactor at a low but accurately controlled rate and on the other to pump cooling water to power station发电厂or refinery炼油厂at a very high rate.l一方面，必须以缓慢但准确控制的速度向 反应器注入反应物或催化剂，而另一方面 要高速向发电厂或炼油厂输送冷却水lThe fluid may be a gas or liquid of low viscosity, or it may be a highly viscous粘性的 liquid, possibly with non-Newtonian characteristics.l流体可能是低粘度的气体或液体，或是高 粘度的液体，也可能具有非牛顿性质。

lIt may be clear清澈的or it may contain suspended particles and be very corrosive腐蚀 的, 腐蚀性的. All these factors因素influence the choice of pump. l流体可能是清澈的，也可能含有悬浮颗粒 ，并具有强腐蚀性，所有这些将影响到泵 的选择lPump design and construction is a special专门 的，专业的field, and manufacturers should always be consult咨询.l泵的设计和结构是一个非常专业的领域， 顾客经常就此请教制造商lIn general pumps used for circulating流动， 循环gases work at higher speeds than those used for liquids, and lighter valves阀门are used.l一般说来，输送循环气体的泵比输送液体 的泵转速要高，可以用较轻一些的阀门lMoreover, the clearances间隙，空隙between moving parts are smaller on gas pumps because of the much lower viscosity of gases, giving rise to引起，使发生an increased tendency for leakage泄漏to occur.l另外由于气体的粘度很小，产生泄漏的可 能性增大，因此气泵运动部件间的间隙应 更小。

lWhen a pump is used to provide a vacuum真空, it is even more important to guard against预防，提防leakage. l当泵用来产生真空时，预防泄漏就更 加重要The work done by the pump is found by setting up建 立an energy balance equation. If Ws is the shaft work轴功done by unit mass单位质量of fluid on the surroundings环境, the –Ws is the shaft work done on the fluid by the pump.l通过建立能量平衡方程就可以得到泵所做的 功如果Ws是单位质量流体对环境所做的轴 功，那么－Ws就是泵对流体所做的轴功l 轴功是系统通过机器轴与外界传递的功 lIn any practical system, the work done by the pump will not be 100 percent efficient效率, and more energy must be supplied by the motor电机，马达driving the pump than is given by-Ws.l在任何实际系统中，泵的效率都不可能达 到100%，驱动泵的电机必须提供比－Ws更 多的能量。

lIf liquids are considered to be incompressible 不可压缩的, there is no change in specific volume比容from the inlet进口to the delivery side出料侧of the pump.l如果认为液体是不可压缩的，从泵的入口 到出口，它的比容就没有变化l 比容:单位质量的物质所占有的容积称为比容，其数值是密度的倒数 lThe physical properties of gases are, however, considerably influenced by the pressure, and the work done in raising the pressure of a gas is influenced by rate of heat flow between the gas and the surroundings. l但是，气体的物理性质受压力的影响很大， 提高气体压力所做的功，受气体与环境间热 传递速率的影响l Thus if the process is carried out adiabatically 绝热地all the energy added to the system appears in the gas and its temperature rises. l因此，如果过程绝热进行，加入到系统中的 能量将存在于气体中，它的温度会升高。

lIf an ideal gas is compressed压缩and then cooled to its initial最初的，原始的temperature, its enthalpy焓will be unchanged and the whole of the energy supplied by the compressor压缩机is dissipated消耗to the surroundings.l如果压缩理想气体，然后冷却到它的初始温度 ，它的焓不变，压缩机提供的全部能量将分散 到环境中l焓H是状态函数 lHowever, if the compressed gas is allowed to expand it will absorb heat and is therefore capable of doing work at the expense of以……为代价 heat energy from the surroundings. l但是，如果让压缩后的气体膨胀，它将吸热， 并消耗从环境吸收的热能而做功lAs already indicated表明，指出, the liquids used in the chemical industries differ considerably in physical and chemical properties, and it has been necessary to develop a wide variety of各种各样的 pumping equipment.l正如已经提到的，化学工业中所用的液体在物 理和化学性质上存在很大的差别，因此需要开 发各种各样的输送设备。

lThe two main forms are the positive正的 displacement位移type and the centrifugal pumps离心泵. l其中的两种主要类型是正位移泵和离 心泵lIn the former, the volume of liquid delivered is directly related to the displacement of the piston 活塞eleme。